1. Field of the Invention
The present invention relates to the field of variable gain amplifiers.
2. Prior Art
Amplifiers having a gain control capability are commonly used in wireless cell phone and other analog circuit applications. In the cell phone case, a signal is received on an antenna, with the strength of the received signal varying to a very large degree as the cell phone moves with respect to the base station (transmitted signal). A simple fixed gain receiver would amplify the variation to provide a widely varying signal to the analog-to-digital conversion circuitry within the cell phone that converts the signal to a digital signal for further processing. Such a wide variation in signal strength would result in an unacceptable error when converted to digital form by the analog-to-digital converter circuitry.
To avoid these problems, a variable gain amplifier is used to adjust the gain in the path of the received signal so that the full available range of the analog-to-digital converter circuitry may be used. In such applications, it is desired to provide a variable gain receive path amplification that produces a logarithmic characteristic in the gain path with a gain control signal such that the decibels of gain is linearly related to the gain control signal VAGC controlling the amplifier stage(s).